Typescript Numeric Literal Types X * Y (Multiplication)

Acid Coder
1 min readJun 30, 2022

We have seen how subtraction works

now can we do multiplication?

yes we can, and this is how you do it, method 1:

type CreateArrayWithLengthX<
LENGTH extends number,
ACC extends unknown[] = [],
> = ACC['length'] extends LENGTH
? ACC
: CreateArrayWithLengthX<LENGTH, [...ACC,1]>
type Multiplication<X extends number, Y extends number, Z extends number[] = []> =
[...CreateArrayWithLengthX<Y>]['length'] extends Z['length']
?[]
:[...CreateArrayWithLengthX<X>, ...Multiplication<X,Y,[1,...Z]>]
type A = Multiplication<526,19>['length'] // 9994
type B = Multiplication<1,48>['length'] // error if 2nd interger exceed 47

playground

method 2:

type CreateArrayWithLengthX<
LENGTH extends number,
ACC extends unknown[] = [],
> = ACC['length'] extends LENGTH
? ACC
: CreateArrayWithLengthX<LENGTH, [...ACC,1]>
type Multiplication<X extends number, Y extends number, Z extends number[] = [], V extends unknown[] = []> =
[...CreateArrayWithLengthX<Y>]['length'] extends Z['length']
? V['length']
: Multiplication<X,Y,[1,...Z],[...CreateArrayWithLengthX<X>,...V]>
type A= Multiplication<19,526> // 9994
type B= Multiplication<526,19> // 9994

limitation: the product cannot exceed 9999 because the max tuple size is 9999

playground

2nd method is better because the 1st method 2nd integer cannot be larger than 47 (method 1 Multiplication is not tail recursion, but still I was expecting it to error at 50, not 48, hmm…)

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Acid Coder

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